The province's Environment Department says the latest tests are expected to show whether work to fix a problem with the mill's power boiler during a shutdown in September has reduced emissions.
Consulting firm Stantec Consulting is carrying out the tests, which are expected to conclude Friday and are required under a government compliance order issued in August.
The legally binding order gives the paper mill in Abercrombie Point near Pictou until May 30 to get its air quality emissions in line or face closure.
Tests conducted in August showed the operation was spewing emissions above legal limits.
The mill's continued operation has angered many Pictou residents, with some calling for its immediate closure until it deals with its aging smoke stacks.